First, because it's completely free, as long as you use it for personal use. Not only free, it's also open source. What does it mean? You can develop it to suits your need. Off course then you wouldn't be a beginner like me if you start doing some software development.
As I mentioned before, there are thousands of R package at your disposal. Most of them, as I have followed, are made by professors, PhD and master students. So you just need to choose which one is the most suitable to solve your problem.
Secondly because R is multiplatform. It runs on the three major operating systems (OS): Linux (Ubuntu, Debian, Fedora etc), Mac OSX, and off course Windows. As per today, R base has reached version 3.1.1. What is R base? I'll tell the story in a moment.
Thirdly because it's command line. An unfortunate event for some of us who are 'point and click' persons right, including me several years a go. The command liner was not so tempting to learn, not before these two words were introduced globally, 'reproducible research'. Command line makes it easier for you to reproduce the process and extend the analysis, without having to do many screen capturing.
Forthly because R can produce (and reproduce) high quality graphics. Your job to follow The graphic requirements from the editor of scientific journal has never been easier.